The Milky Way Project: Bridging Intermediate- and High-Mass Star Formation with the MIRION Catalog of Yellowballs

TL;DR

The paper introduces the MIRION catalog, derived from Milky Way Project yellowballs, to probe the transition between low-mass and high-mass star formation. It details multiwavelength infrared photometry, CO-based velocities, distance estimation via the Reid calculator, and crossmatching with major star-formation catalogs, yielding a large IMSFR-enriched dataset (∼6176 sources; ∼94% with distances). The results show most MIRION sources are compact photodissociation regions within clumps spanning $0<\log_{10}(M/M_\odot)<4$ and $1<\log_{10}(L/L_\odot)<5$, with color diagnostics indicating distinct environments for IMSFRs versus high-mass SFRs. The study demonstrates robust crossmatching and quality control, highlights the prevalence of IMSFR signatures, and outlines a path for using IR colors to predict star-forming properties in a follow-up analysis, aided by classroom PERYSCOPE measurements.

Abstract

We describe the construction and use of the Mid-InfraRed Interstellar Objects and Nebulae (MIRION) catalog, which was compiled from 6176 objects identified as "yellowballs" (YBs) by participants in the Milky Way Project. The majority of YBs are compact photodissociation regions generated by intermediate- and high-mass young stellar objects that are embedded in star-forming clumps ranging in mass from ten to one million solar masses and luminosity from ten to ten thousand solar luminosities. The MIRION catalog increases the number of candidate intermediate-mass star-forming regions (SFRs) by nearly two orders of magnitude, providing an extensive database with which to explore the transition from isolated low-mass to clustered high-mass star formation. The catalog comprises five tables that include mid- and far-infrared photometry; velocities of source-associated molecular clouds; distances to these molecular clouds; physical properties of source-associated star-forming clumps; and source crossmatches with other catalogs. The structure of the catalog enables users to easily sort objects for further study based on distance or environmental properties. Our preliminary analysis extends our earlier findings that indicate a relationship between IR colors and the physical properties and evolutionary stages of SFRs. Photometry will be periodically updated online to incorporate measurements from volunteers participating in a classroom activity known as the People Enabling Research: a Yellowball Survey of the Colors Of Protostellar Environments (PERYSCOPE) Project. These updates will continue to refine the IR flux measurements and reduce photometric errors. A follow-up paper will present a detailed analysis of how IR colors can be used to predict the properties of star-forming environments.

Figures (9)

• Figure 1: Output images from the Python-based photometry tool used in this work. Upper left panel (A) shows the region containing the source and background emission, where the black circle shows the original MWP average user-selected YB center and radius. Upper right panel (B) shows a user-selected mask covering the source. Bottom left (C) shows the interpolated, background-only image. Bottom t (D) shows the background-removed, source-only image used for photometry.
• Figure 2: Representative examples of sources to which flags were applied. All images shown are 8 $\mu$m background-subtracted, source-only with the exception of (B) which shows the original region since the source-only image which is not meaningful in this case. (A): multiple sources within the masked region. (B): no obvious source at that wavelength. (C): photometry flagged for poor confidence, in which the background subtraction left a negative-valued region near the source, (D): a very round, extended structure.
• Figure 3: Example MIRION sources showing the different flags used for spectral classification. The top panel shows a SP source, where only one CO peak exceeds 0.8$I_{max}$. The middle panel shows a case where a secondary peak exceeds 0.8$I_{max}$, marking it as a MP: 1 source. Lastly, the bottom panel shows a source associated with a dense gas tracer (DGT). In this case, the secondary peak coincides with a 1662 MHz OH maser from THOR, and is preferentially adopted over the CO peak with the most intense emission.
• Figure 4: Physical properties of MIRION catalog--Hi-GAL matched sources. Lower-left and upper-row histograms show values from Elia2021 rescaled using our newly calculated distances. The lower-right panel shows the distance-independent luminosity-mass ratio from Elia2021. Smaller histograms show the distribution of properties for MIRION objects with clear signatures of massive star formation. See text for full discussion.
• Figure 5: As Figure \ref{['fig:histo1']}. All quantities plotted are distance-independent.